1. Field of the Invention
The present invention relates to a color thermal printer in which color thermosensitive recording material is fixed by ultraviolet rays. More particularly, the present invention relates to an improvement of a color thermal printer in which ultraviolet rays for the fixation can be controlled effectively.
2. Description Related to the Prior Art
A color thermal printer, as disclosed in U.S. Pat. No. 4,734,704, is used with color thermosensitive recording material, which consists of cyan (C), magenta (M) and yellow (Y) thermosensitive coloring layers formed on a support. The printer applies heat to the recording material to record a full-color image thermally in direct fashion. One of the coloring layers disposed on an obverse of the recording material is subjected to the thermal recording at first. The thermal recording is performed through the coloring layers successively in the order toward the support or the reverse of the recording material. Should a coloring layer be not fixed, it would receive unwanted extra heat from the subsequent thermal recording. Any coloring layer must be fixed before a subsequent layer can be subjected to the thermal recording. For the fixation of each coloring layer, ultraviolet rays in a range of a predetermined wavelength are applied to the layer directly after the thermal recording, to destroy the coloring ability of the layer.
The color thermal printer has a platen drum on which the recording material is supported. The platen drum is rotated at a regular speed. During one rotation, the thermal recording and the optical fixation are performed. A speed of the rotation of the platen drum is determined in consideration of heat sensitivity of each coloring layer.
If the speed of the platen drum is determined somewhat high in consideration of the thermal recording, there is an occasion in which the rotation commonly used for the fixation is excessively fast. There is a problem in that ultraviolet rays applied in the rotation are insufficient for fixing the coloring layer to destroy the coloring ability.
If the speed of the platen drum is determined somewhat low for the thermal recording, there is an occasion in which the rotation is too slow for the fixation. The ultraviolet rays applied in the rotation are excessive for the fixation. There is a problem in that a weaker component included in the ultraviolet rays unexpectedly fix a subsequent or final coloring layer. The image quality of the color thermal recording is seriously influence.